Cluster
Flies
Location: Numerous locations, but usually in lofts and roof spaces.
South-facing walls often favoured.
Detection: Visual
sightings of large numbers of adults.
There are three
main species of fly collectively known as cluster flies. They
are Musca autumalis, a small fly of about the same size
and colour as the house fly, Pollenia rudis, a larger fly
dull brown/grey in colour, and lastly Dasyhora caynella
which is about house fly size and shiny green/blue in colour.
Biology:
Cluster flies, particularly
Pollenia rudis are very common occurring throughout Great Britain.
The adult flies after hibernation during the winter months, lay
their eggs in the earth or in animal dung. Permanent areas of
grassland are favourite sites e.g. permanent grazed pasture or
parkland as solid cultivation such as ploughing disrupts the flies
breeding cycle. The eggs remain in the earth and hatch when soil
temperature increases in the spring. The larval stage is parasitic,
entering earthworms and feeding upon them until emerging as an
adult fly.
Cluster flies migrate
from outdoors into the lofts of houses and farm buildings during
the winter months. Obvious signs of an infestation is a roof space
containing a large quantity of lethargic flies and a quantity
of dead flies. Unless the loft is used for storage purposes or
is accessed regularly the flies will hibernate successfully leaving
in early spring dependent on the weather.
Reasons for control:
Cluster flies are
not damaging to property when they enter buildings in the autumn
purely to hibernate over the cold winter months. As mentioned
above they feed on decaying vegetation and earthworms. Cluster
flies are not to be associated with dead animal bodies, faeces
and the resulting maggots. Fibre glass insulation material in
lofts can look unsightly if covered with the bodies of flies that
have not hibernated successfully although its insulation properties
will not be altered and no damage to the roof structure will occur.
If the loft is home
to a hibernating colony of flies, first floor lighting diffusers
or sunken spot light lenses can become full of dead or dying flies.
This often occurs in houses where the loft area has been converted
into a living room. In most buildings built after 1950, the external
roof covering has an under felt layer. Cluster flies can successfully
hibernate undetected between these two layers. Often cluster flies
can be seen basking on sunny grassland or resting on south facing
walls of buildings. Cluster flies, like birds, return to roof
spaces previously occupied so re-infestation is almost inevitable.
Control/Treatment:
Insecticidal space spray by us
or another pest control company (N.B. if bats are present in your
loft/attic this will not be possible). If you are not in our area
please see the BPCA's web site to locate a pest control company
near you search
BPCA member.
The use of fly control units
also works well (N.B. it is not recommended that electric grid
machines are used in loft areas/roof voids, however if you wish
to use this type of machine it is important that these are used
with an extra deep cluster tray and checked on a regular basis).
Please see our online eshop www.hygieneshop.co.uk
for fly killer units which are suitable for controlling cluster
flies.
Below photo shows a glueboard covered in cluster
flies:-
N.B. If bats are present in the
roof space, then it is not recommended that any sort of fly control
is used.
